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SimDemon

About mass and weight...

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SimDemon    122
This is a question I have been thininkg about for a couple days. I would like to know what the difference between mass and weight is. Also, what unit is mass measured in? (Newton(N), Kilogram(kg), etc.) Thanks, Matt Utley If thispost = 0 Then GoBack() Else Read() End If

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Null and Void    1088
From the dictionary: Mass:
A property of matter equal to the measure of an object''s resistance to changes in either the speed or direction of its motion. The mass of an object is not dependent on gravity and therefore is different from but proportional to its weight.

Weight is the force applied by gravity to a body with mass. Mass is measured in grams, weight is measured in newtons (it''s a force, after all).

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Guest Anonymous Poster   
Guest Anonymous Poster
Weight is the force due to gravity on an object. The formula for weight is w = mg. Weight is measured in newtons like any other force. Mass is measured in kg.

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spiffgq    122
In the American system of units, both mass and weight are commonly measured in pounds. Technically, pounds are weight and slugs are mass. Just like in metric, mass and weight are measured in kilograms. Technically, Newton is weight and grams are mass.

On earth, your weight is X and your mass is Y. Fly to the moon. Now your weight is Z and your mass is still Y. You weight can change depending on where you are, but your mass will always remain the same (more or less ).

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SimDemon    122
I think I got this right. Ok, if I know the weight, I can get the mass by mass=weight/gravity, right? Now, If I figure out the mass, and I need to know how much force is needed to move an object it would be like this, right?

F=(object.mass * object.accel);

What I have learned in school is that the force you use has to be greater than that found in F=ma. Because if your force is equal to the force required, they are balanced, causing the object you are trying to move to stay still, which is called balanced forces. Is all of this right, or am I just a crazy guy?

Thanks,
Matt Utley

If thispost = 0 Then
GoBack()

Else
Read()
End If

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Fruny    1658
Σ F = m.a ... You have to sum all forces. When all the forces cancel each other (e.g. lift+gravity+thrust+drag in a plane) ... the acceleration is nil, and you have an equilibrium (the plane keeps going at the same speed).

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Guest Anonymous Poster   
Guest Anonymous Poster
If you want to accelerate on object you must apply a force greater than the static friction on the surface. To find out the acceleration of the object use this formual:

F(applied to object) - F(friction) = ma

F(friction) = uF(normal)

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Zipster    2365
And that u represents the coefficient of friction for the object. Basically, you need to look it up from a big table for your substance, there''s no easy way to find it (unless you already know the force of friction that is, but that''s what you''re trying to solve).

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Timkin    864
quote:
Original post by SimDemon
I think I got this right. Ok, if I know the weight, I can get the mass by mass=weight/gravity, right? Now, If I figure out the mass, and I need to know how much force is needed to move an object it would be like this, right?

F=(object.mass * object.accel);

What I have learned in school is that the force you use has to be greater than that found in F=ma. Because if your force is equal to the force required, they are balanced, causing the object you are trying to move to stay still, which is called balanced forces. Is all of this right, or am I just a crazy guy?



Putting aside the discussions on friction and resistance for a moment... yes Matt, you are correct. The state of having all external forces on an object in balance is called equilibrium .

On the issue of weight and mass, people erroneously believe that their bathroom scales measure their weight. They don''t. Bathroom scales are a form of mass balance, based on a carefully calibrated spring (or solid state transducer in modern scales), which measures the mass of a person, based on a uniform assumption that g=9.81 m/s2. So, in fact, when you look at the scales next time, you can tell yourself that you actually weight about 10 times more than the number on the display! As pointed out (in metric), mass is measured in kilograms and represents the amount of matter in an object, while weight is measured in Newton''s and represents the force required to accelerate the object at a rate equivalent to the local gravitational field. We are just so used to talking about weight while we are standing on Earth, that is has become synonymous with acceleration due to gravity on the Earth''s surface (i.e., 9.81 m/s2).

Cheers,

Timkin

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dMDI    122
Mass is the amount of matter in an object, and also the property of that object that resists changes in motion.

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